Biochar (the solid, carbon-rich co-product of biomass pyrolysis), in addition to carbon sequestration, soil amelioration and improvement of plant performance, can significantly reduce the severity of foliar and soil-borne diseases in various crops.
Nevertheless, the mechanisms associated with soil-borne disease suppression are not fully understood.
This study tested the effects of two contrasting biochars at concentrations of 0-3% (w/w) on fusarium crown and root rot (FCRR) of tomato caused by Fusarium oxysporum f. sp. radices-lycopersici (FORL) and the mechanisms of disease suppression.
We found that biochar suppressed FCRR of tomato at higher biochar concentrations by up to 79%. The mechanism of disease suppression could not be explained by direct toxicity, as no significant mycelium radial growth inhibition was detected by either biochar up to 3% in an in-vitro assay.
Biochar amendment significantly increased the counts of culturable general bacteria, but had no effect on filamentous fungi counts.
PCR-DGGE analyses of the 16S rRNA gene showed substantial differences in rhizosphere bacterial composition between biochar-amended and control non-amended soils.
The enrichment of bacterial abundance, beneficial microorganisms and shifts in microbial community structure may play important roles in the overall effects of biochar on disease suppression either through direct antagonist effects towards pathogens or indirectly via induction of systemic resistance in the plant.